The present invention relates to conveyors and, in particular, to power and free conveyors. Specifically, the invention relates to trolley stop assemblies which are used to disengage trolleys from a dive system, stopping the trolley at selected places along a conveyor track. The trolley stop assembly of the instant invention is particularly developed for use with otherwise conventional inverted power and free trolley systems.
Conventional power and free trolley conveyors are characterized by a transport mechanism which includes a trolley mounted on rollers or the like for movement along a track or rail system. Generally, such trolleys have a member extending therefrom which is engaged by a dog member on a drive, such as a chain drive or similar drive, to convey momentum to the trolley. In a power and free system, the trolleys may sometimes roll along the tracks freely, even when the dog member on the drive does not engage the trolley. For example, the trolley may be allowed to freely roll during a downhill slope, when going around a curve, or when being transferred between chain drives. Further, disengagement between the trolley and the drive dog may be desired at points when the trolley is to be stopped, as for example when maintenance, construction, or repair access to an object being transferred by the trolley is desired.
Generally, in such systems a carrier member is mounted upon the trolley. The carrier member may vary considerably, depending on the nature of the objects to be transported. It will be understood that a variety of carrier members may be used in association with the present invention.
For conventional systems, the term "inverted" as in "inverted power and free conveyors" refers to the fact that the drive mechanism which engages the extending member on the trolley, generally runs beneath the track and the trolley. In many conventional systems, the drive mechanism comprises a continuous chain drive with upwardly extending drive dogs thereon. The drive dogs for inverted systems engage a depending member on the trolley to push same. Herein, the extending member on the trolley will be referred to as the trolley dog and the dog on the drive system as a drive dog or pusher dog.
In many conventional systems the trolley dog is vertically movable between upper and lower positions. When in the lower or engaged position, the trolley dog depends low enough to be engaged by pusher dogs being driven underneath the trolley by means of the drive mechanism. On the other hand, when the trolley dog is in the upper or disengaged position, it is generally too high to be reached by the upwardly extending drive or pusher dogs. Therefore, when the trolley dog is in the upper position, the trolley is not positively engaged and driven.
Many conventional trolley stops operate by selectively moving the trolley dog between engaged and disengaged positions. Generally, for such systems, the trolley dog has a forward cam surface which, when it engages the trolley stop, is cammed upwardly until disengagement with the drive dog is achieved. Typical conventional trolley systems operate by providing, selectively, an obstruction in the path-of-motion of the trolley to cause the camming of the trolley dog to an orientation out of engagement with the pusher dog.
For example, a conventional trolley stop arrangement may utilize a knife blade extending perpendicular to the track of the trolley, sometimes extending completely thereacross, to be engaged by the trolley dog. The knife blade, when withdrawn, does not block the path-of-motion of the trolley dog, and thus the trolley will pass the trolley stop under positive drive. On the other hand, when the blade is extended into the path of the trolley dog, it will be engaged thereby, with the camming action lifting the trolley dog and bringing the trolley to a stop.
Such conventional trolley stops, while they have been somewhat effective, have not been completely satisfactory. First, such knife blade arrangements often require portions which extend outwardly from the side of the track or conveyor body. That is, often a piston for operating the knife blade, a linkage system, or a receptacle for receiving the knife blade, when retracted, extends substantially outward from the side of the track. This not only takes up space which might be more conveniently used, but also provides inconvenient and potentially hazardous obstructions to vehicles or personnel moving closely along the side of the conveyor track.
Further, such systems have not, in the past, satisfactorily provided for positive braking of the trolley. That is, a primary reason that the trolley comes to a stop is that the trolley dog has become disengaged from the drive dog. Further, the friction of the trolley dog rubbing against the knife blade does tend to bring the trolley to a stop. However, generally satisfactory positive braking is not achieved with such a system.